542 BOTANY AND PHARMACOGNOSY. 



of dark-brown periderm ; inner surface yellowish-brown, coarsely 

 striate and fissured longitudinally, and with detachable bast fibers ; 

 fracture uneven, coarsely fibrous, surface porous and dotted with 



Fig. 237. White oak bark with the fissured corky layers (bork) still present. 



groups of white sclerench3miatous cells and fibers ; odor slight ; 

 taste astringent (Figs. 237; 300, B; 301, A). 



Constituents. — Tannin about 10 per cent. ; starch and cal- 

 cium oxalate. The tannin yields upon sublimation a crystalline 



